Method for the conversion of carbonaceous solids into volatile products



Jan. 15, 1952 z MARTlN 2,582,710

' H. METHOD FOR THE CONVERSION OF CARBONACEOUS SOLIDS INTO VOLATILE PRODUCTS Filed Sept. 28, 1946 FD-E5H Powoaxzeu COAL.

Homer martin inventor Patented Jan. 15, 1952 I T D STATES PATENT.f F'FICETI-ff I METHOD FOR mz fi zrssmer cAR-I 1 I I I V BONACEOUS SOLIDS PRODUCTS IN'ro VOLATILE Homerv Z. Martin, Roselle, N. J., assignor to 7 Standard Oil Development ration of Delaware Company, a corpoa Application September 2a, 1946, Serial No. 699,949

' 9 Claims. 1

The present invention relates to the conversion of carbonaceous solids into volatile products by carbonization and/or gasiflcation with oxidizing gases and/or steam. More particularly, the invention is concerned with the pretreatment of carbonaceous solids such as all types of coal. lignite, cellulose materials, including lignin, oil

shale, tar sands, coke, oil coke, etc. which are tov 1000 F. depending on the character of the coal and the conditions of the subsequent conversion process. The conventional method of generating and supplying this preheat to the coal involves the combustion of combustible gases with air in a separate heater and passage of the hot flu gases over the coal to be preheated.

In order to avoid losses of volatile coal constituents and to prevent baking and sticking of the coal in the preheating zone, the inlet temperature of the gas must not exceed about 1000"- 1400" F. In addition, the specific heat of the flue gas is only a small fraction of that of the coal to be heated. As a result, the coal must be preheated to an undesirably high temperature and thereafter quenched to the desired temperature or vast amounts flue gases are required to heat coal of atmospheric temperature up to a desir-' ditions not only constitute a serious load on process economies but frequently cause even serious operational difflculties.

The present invention overcomes the aforementioned difliculties and afiords various additional advantages. These advantages, the nature of the invention and the manner in which. it is vention to 'provide improved means for preheating carbonaceous solids to be subjected to a conversion into volatile. products at elevated temperatures.

Another object of myinvention is to provide a improved method and apparatus for uniformly preheating carbonaceous solids to a definite desired temperature, preliminary to-a high temperature treatment of said solids.

A more specific object of'my invention is to provide improved means for pretreating, particularly preheating carbonizablesolids, at uniform temperature below the temperature of beginning softening and carbonization.

Other and more specific objects-and advantages of my invention will appear hereinafter.

In accordance with my invention, the carbonaceous solids to be pretreated are maintained in ment is generated in a combustion zone. surrounded by and in open communication with said bed so as to permit circulation of carbonaceous solids through said combustion zoneifrom and to said fluidized bed of solids and of combustion products from said combustion zone to said fluidized bed.

In this manner, the heat generated by the combustion is immediately transferred to a portion of the carbonaceous solids which serve as solid heat carrier of high specific heat thus reducing to a minimum the volume of hot flue gases required for preheating. In addition, the excellent heat transfer and distribution characteristics of the dense turbulent fluidized bed of solids to be pretreated and the directheat exchange between the combustion zone and the fluidized solids bed make it possible to maintain a temperature differential as low as about '100-400 F. between the heat-generating combustion and the fluidized solids bed to be heated, resulting in the elimination of undesired high temperature side reactions. The pretreated carbonaceous solids are recovered in the form of fluidized or fluidizable solids and are, as such, particularlysuitable as charge for conversion processes employing the fluid solids technique.

The combustion zone may be operated so as to generate merely the heat required for preheating. However, by a suitable choice of thetemperature and size of the combustion zone, a suitable choice of the gases supplied to the combustion zone, and a proper control of the rate of circulation of carbonaceous solids through the combustion zone it may simultaneously serve to dehydrate, carbonize, gasify and/or mildly oxidize the carbonaceous solids passed therethrough.

The fuel burnt in the combustion zone preferably consists of combustible constituents of the carbonaceous solids circulated therethrough from the dense fluidized mass of solids to be pretreated. However. if it is desired to avoid a loss of combustible constituents of the solid carbonaceous charge, an extraneous fuel of lower ignition temperature such as a fuel gas or fuel oil may be charged to the combustion zone along with the air and/or oxygen supporting the combustion. If these fuels are added in theoretical or slight excess proportion to the oxygen supplied, little or no combustible constituents of the solid carbonaceous charge will be burnt and the latter will act mainly as a heat carrier.

Having set forth the general nature and objects, the invention will be best understood from the more detailed description hereinafter, in which reference will be made to the accompanying drawing which illustrates semi-diagrammatically a system suitable for carrying out a preferred modification of the present invention.

Referring now in detail to the drawing, the system shown therein essentially comprises a pretreating chamber l adapted for fluid solids operation and a vertical combustion zone 30. The function and cooperation of these elements will be explained hereinafter in connection with the preheating of a bituminous carbonization coal from substantially atmospheric temperature to about 600 F. to prepare it for subsequent low temperature carbonization at about 800 to 1200 F. It should be understood, however, that any other solid carbonaceous charge previously mentioned may be treated for the same or different purposes in a generally analogous manner.

In operation, finely divided bituminous carbonization coal having a volatile content of about 20 to 35%, a plasticizing temperature of about 700 F. and a temperature of incipient carbonization of about 750 F. is supplied through pipe I to pretreating chamber I 0. The coal should have a fiuidizable particle size which may fall within the broad range of about 50-400 mesh, 100-200 mesh being preferred, though larger sizes up to about in. may be used. Pipe I may be part of any conventional feeding device for fluidizable solids such as an aerated standpipe, pressurized feed hopper, mechanical conveyor or the like. The finely divided coal forms in chamber III a dense turbulent bed 20 of solids fluidized by upwardly flowing gases to resemble a boiling liquid having a well defined upper level L10 as will appear more clearly hereinafter.

Chamber i0 is equipped, in its lower portion, with a horizontal plate l2 provided with preferably adjustable orifices M which permit a controlled passage of finely divided coal from bed 20 toa point below the bottom of combustion zone 30. A fluidizing gas such as steam, flue gas, or the like is introduced into bed 20 through several, preferably annular, perforated tubes l6 located above and in close proximity to plate l2. The amount of fluidizing gas thus supplied is preferably so controlled that the gas has a linear velocity of about 0.3-3 ft., preferably about l-2 ft. per second within bed 20 to convert the latter into the desired dense ebullient mass of solids,

" 4 The fluidizing gas may simultaneously serve as a stripping agent to remove occluded undesirable gases from the solids to be passed to combustion zone 30 as will be presently explained. 5 Coal particles .passlng through orifices M in plate I2 into lower zone'25 of chamber III are.

aerated and kept in a mobile turbulent state by an aeration gas such as air, oxygen, steam, flue gas, or the like supplied through taps [8' at a linear velocity of about 0.3 -3 ft. per second. The bulk of the air and/or oxygen required for combustion is introduced through line 5 directly into the lower, open end of combustion zone 30 at a relatively high superficial velocity of about 320 ft. per second, so as to establish an ejector, effect at the bottom of zone 30, whereby coal particles are forced into and upwardly through combustion zone 30. The upper end of combustion zone 30 is preferably provided with a perforated cover plate 32 which permits the passage of solids and gaseous combustion products from combustion zone 32 into bed 20 while effectively preventing solids from entering the top of combustion zone 30.

The temperature of combustion zone 30 may be controlled by the oxygen content and linear velocity of the gas supplied through line 5, the latter determining in combination with the opening of orifices M, the rate of fuel supply to zone 30. For the purpose of preheating coal bed 20 to about 600 F. the temperature in zone 30 is maintained at about 800-1000 F. The amount of air required may vary within wide limits depending on the relative sizes of chamber l0 and zone 30, the character of the carbonaceous charge and the pretreatment desired. For the preheating of coal as indicated above in a system wherein the ratio of the diameters of chamber l0 and zone 30 falls within the approximate range of 2-10:l, about 0.1 to 5 cu. ft. of air supplied at a linear velocity of about.4-l0 ft. per second in zone 30 is generally adequate to preheat 1 lb. of coal from about 60 to about 600 F. The solids-in-gas suspension within combustion zone 30 may have an apparent density of about 1 to lbs. per cu. ft. as compared with a density of about to 30 lbs. per cu. ft. of bed 20. At these conditions about 0.005 to 0.01 lb. ofcombustible coal constituents are burnt in zone 30 per pound of coal to be preheated.

A dilute suspension of solid combustion residue in flue gases passes through cover plate 32 at the temperature of combustion zone 30 and enters the fluidized bed which absorbs the sensible heat 55 of the combustion products uniformly through its entire mass to attain the desired uniform temperature of about 600 F. It should be understood that the pseudo-hydrostaticpressure generated by the fluidized solids column between plate l2 and the top of zone 30 must be great enough to overcome the flow resistance through orifices l4, combustion zone 30 and perforated plate 32. On the other hand, the length and cross-section of combustion zone 30 should only 65 be fractions of those of chamber I so that the bulk of the treatment of carbonaceous charge takes place within bed 20. In general, the ratio of the heights of vessels It) and 30 may be about 2-10:1, preferably about 8:1. and the ratio of 7 their diameters about 2-10:1, preferably about Spent flue gases are withdrawn overhead from level Lin and passed through line I to the atmosphere or any desired use, such as heat recovery,

7 aeration, etc., if desired, after separation and reaceamo turn to bed 20, of entrained solids fines by means of a conventional gas-solids separation system including cyclones and/or electricalprecipitators. or the like. Preheated fluidized coal is withdrawn from bed 20 through a conventional standpipe or any other conventional conveying means for fluidized solids and passed substantially at the temperature of bed 20 to any subsequent processing stage such as carbonization. producer or water gas manufacture, etc.

If desired, an extraneous fuel, preferably a fuel gas or fuel oil may be introduced through line 35 into air pipe at a point close to its entrance into combustion zone 30. This extraneous fuel supply may be so controlled that it consumes substantially all of the oxygen available for combustion leaving the combustible constituents of the carbonaceous solids entering zone 30 unbumt.

It will be understood that the temperature levels at which zone 30 and bed are operated may be substantially higher or lower than those indicated above. operated at about 400-600 F. if mere dehydration of the coal in bed 20 at temperatures of 200-300 F. is desired. On the other hand, the temperature of zone may be raised to 1200-1500 F. in order to cause carbonization of the carbonaceous charge in bed 20, or to temperatures in the neighborhood of 2000 F. when it is desired to convert the solids of bed 20 into producer or water gas with the aid of air and/or steam supplied through pipes l6. Bed 20 may also serve as a zone of mild oxidation at temperature conditions similar to those indicated above for preheating when a suitable amount of oxygen or air is added to the gas supplied through pipes I8. In all these cases the temperature differential between zone 30 and bed 20 as well as the absolute temperature levels may be additionally controlled by choosing a suitable ratio of fresh carbonaceous solids feed to bed 20 to the combustion rate in zone 30.

As previously indicated, zone 30 may also be operated as a conversion or treating zone proper such as a carbonization or gasiflcation zone rather than as a mere heat-generating zone. For this purpose, the dimensions of zone 30 are increased in relation to chamber l0 and the linear velocity of the gases flowing through zone 30 is decreased so as to permit the treatment of a more substantial proportion of the total solids charge per unit of time at the conditions of zone 30. For example, zone 30 may have about the diameter and about /2 the height of chamber l0 and the linear gas velocity within zone 80 may be about 2-4 ft. per second as compared with a gas velocity of about 0.5-1.5 ft. per second in bed 20, the relative and absolute temperatures in zone 30 and bed 20 being controlled by the supply of oxygen and, preferably, of extraneous fuel, in cooperation with a control of the ratio of fresh solids feed to bed 20 and zone 30.

The temperature conditions and reactants required for these various conversions are those known in the art and need not be here specifically enumerated. However, it is noted that whenever a substantial amount of condensible volatile products such as tar is produced in zone 30 the vapors of such condensible products should be separated from entrained solids in conventional gas-solids separators, preferably at a temperature close to that of zone 30, prior to the return of the solids to bed 20 in order to prevent condensation of tar or the like in bed 20. Whenever zone 30 serves as a conversion zone, the car'- F'or example, zone 30 may be.

6 bonaceous charge is simultaneously dried and ga-eheated and. if desired, mildly oxidized in bed In some cases, it may be desirable to heatinsulate zone 30 as indicated at 3| in order to increase the temperature differential between zone 30 and bed 20. This insulation is of particular value during the starting up period of the process which requires preheating of the fluids supplied through line 0 beyond the ignition temperature of the fuel used in zone 30.

While I have shown combustion zone 30 as a vertical cylinder and this is the preferred embodiment of my invention, zone 30 may be arranged horizontally or it may have the shape of tube bundles or any other suitable shape without deviating from the spirit of my invention.

It will be understood that my process may be made fully continuous by continuously feeding and withdrawing carbonaceous solids through lines 'I and 9, respectively, and continuously feeding fluids supporting the combustion through line I.

My invention will be further illustrated by the following specific example.

Example Chamber 10, total height 13.200 s. c. f./hr. Chamber 10, inner diameter Zone 30. total height Zone 30, inner diameter- Air feed rate Linear gas velocity in zone 30 10 ft./sec. Bed density in zone 30 1.5 lbs./c. i'. Aerating steam inlet temperature---" 300 F. Aerating steam feed rate 1.380 lbs./hr. Linear gas velocity in chamber 10 1.25 ft./sec.

Bed density in bed 20 20 lbs./c. f. Solids circulation rate through zone 30- 7 tons/hr. Temperature in zone 30 Coal burned -130 lbs./i1r.

While the foregoing description and exemplary operations have served to illustrate specific applications and results of my.invention, other modifications obvious to those skilled in the art are within the scope of my invention. Only such limitations should be imposed on the invention as are indicated in the appended claims.

I claim:

1. The method of treating carbonaceous solids at an elevated temperature, which comprises maintaining in a treating zone a dense turbulent bed of finely divided solids having a particle size predominantly within the range of about 50-400 mesh fluidized by passing a gas upwardly through the carbonaceous solids at such velocity within the approximate range of 0.3-3 ft. per second that a lower dense fluidized phase having an apparent density of about 15-30 lbs. per cu. ft. and a superimposed dilute phase separated by an interface are formed, burning a fuel in a combustion zone separated from, confined within, and in open communication with, said bed at a temperature substantially higher than said elevated temperature, supplying solids from said bed to said combustion zone, passing a gas u'pwardly through said combustion zone into said bed at a linear velocity within said combustion zone of the-order of about 10-20 ft. per second 7 and sumciently high to maintain the apparent density of said solids in the neighborhood of about 1-2 lbs. per cu. ft., whereby carbonaceous solids in said combustion zone are entrained and carried by said second named gas in the form of a relatively dilute phase through said combustion zone into said bed, and controlling the temperature of said combustion and the supply of solids to said combustion zone so that the sensible heat of products of combustion and entrained solids entering said bed from said combustion zone is suflicient to heat said bed to said elevated temperature.

2. The process of claim 1 in which the velocity of said second named gas is about 10 it. per second.

3. The method of claim 1 wherein said solids are entrained in and carried by said second named gas through said combustion zone under the pseudo-hydrostatic pressure of said bed.

4. The method of claim 1 wherein said combustion is supported by combustible constituents of said entrained solids.

5. The method of claim 1 wherein said combustion is supported by an extraneous fuel having an ignition temperature lower than that of said entrained solids.

6. The method of claim 1 wherein said second named gas contains the oiggen required to support said combustion.

'l. The method oi claim 1 wherein said solids are carbonizable and said elevated temperature REFERENCES CITED The following references are of record in the file of this patent:

} UNITED STATES PATENTS Number Name Date 1,869,949 Szikla Aug. 2, 1932 1,993,198 Wisner Mar. 5, 1935 2,367,351 Hemminger Jan. 16, 1945 2,378,342 Voorhees et a1 June 12, 1945 2,431,632 Brandt Nov. 25, 1947 2,445,327 Keith July 20, 1948 

1. THE METHOD OF TREATING CARBONACEOUS SOLIDS AT AN ELEVATED TEMPERATURE, WHICH COMPRISES MAINTAINING IN A TREATING ZONE A DENSE TURBULENT BED OF FINELY DIVIDED SOLIDS HAVING A PARTICLE SIZE PREDOMINANTLY WITHIN THE RANGE OF ABOUT 50-400 MESH FLUIDIZED BY PASSING A GAS UPWARDLY THROUGH THE CARBONACEOUS SOLIDS AT SUCH VELOCITY WITHIN THE APPROXIMATE RANGE OF 0.3-3FT. PER SECOND THAT A LOWER DENSE FLUIDIZED PHASE HAVING AN APPARENT DENSITY OF ABOUT 15-30 LBS. PER CU. FT. AND A SUPERIMPOSED DILUTE PHASE SEPARATED BY AN INTERFACE ARE FORMED, BURNING A FUEL IN A COMBUSTION ZONE SEPARATED FROM , CONFINED WITHIN, AND IN OPEN COMMUNICATION WITH, SAID BED AT A TEMPERATURE SUBSTANTIALLY HIGHER THAN SAID ELEVATED TEMPERATURE, SUPPLYING SOLIDS FROM SAID BED OT SAID COMBUSTION ZONE, PASSING A GAS UPWARDLY THROUGH SIAD COMBUSTION ZONE INTO SAID BED AT A LINEAR VELOCITY WITHIN SAID COMBUSTION ZONE OF THE ORDER OF ABOUT 10-20 FT. PER SECOND AND SUFFICIENTLY HIGH TO MAINTAIN THE APPARENT DENSITY OF SAID SOLIDS INTHE NEIGHBORHOOD OF ABOUT 1-2 LBS. PER CU. FT., WHEREBY CARBONACEOUS SOLIDS IN SAID COMBUSTION ZONE ARE ENTRAINED AND CARRIED BY SAID SECOND NAMED GAS IN THE FORM OF A RELATIVELY DILUTE PHASE THROUGH SAID COMBUSTION ZONE INTO SAID BED, AND CONTROLLING THE TEMPERATURE OF SAID COMBUSTION AND THE SUPPLY OF SOLIDS TO SAID COMBUSTION ZONE SO THAT THE SENSIBLE HEAT OF PRODUCTS OF COMBUSTION AND ENTRAINED SOLIDS ENTERING SAID BED FROM SAID COMBUSTION ZONE IS SUFFICIENT TO HEAT SAID BED TO SAID ELEVEATED TEMPERATURE.
 9. THE METHOD OF CLAIM 1 WHEREIN SAID ELEVETED TEMPERATURE IS AT LEAST 800* AND NOT SUBSTANTIALLY HIGHER THAN 2000* F. AND SAID FIRST NAMED GAS CONTAINS STEAM. 